yet another AC question

88 k2500, 350 TBI.... what does the single wire connector on the back of my A/C compressor do? an inadvertant slip of the wrench managed to clean it off of the back of the compressor and I'd like to get the AC going again (hasn't worked since before I broke that conector off). jumping the pressure switch engages the clutch, and there is some freon in it, not sure if it's enough for the system though.

-Bret